Underwater bike gears
 

Hi folks, My son is building a human powered submarine for a race in June and we are using a mountain bike as the basis for the drive train. The frame is aluminum but we are worried about steel bearings rusting out. Looking for any help/ advice on how to vonvert for underwater use. We thought ceramic bearings might be a start.

One time use you'll probably be just fine greasing the crap out of things with marine grease

If you are looking for things to last there are solid oil bearings (or whatever they call them) that have the bearings encased in a oil filed polymer which might work or ceramic bearings could work there are certainly plenty of things that use bearings under water. SKF and NSK make solid oil bearings and stuff for underwater I would reach out to them once you have sizing and see what is possible. If just using it once then yeah what dedhed said will keep you enough out of the red and if you put some big bags on your sled they might call you a Fred just make sure they are waterproof or they will sink you instead.

Fresh water or salt? There's an order of magnitude difference between the two. In salt, you might well need zincs in contact at key places to save the less noble metals. I've spent a lot of time around boats and salt water but mine were always lightweight racing sailboats and the metals were marine aluminums and passive stainless steels. I wish my dad was still around to help you. He had an ocean going sailboat with lots of metal and kept it (in very good shape) for 30 years.

The first decision is whether you're considering a dry boat (air filled) or a flooded design. The following is for s dry boat.

The secret is in having a decent design that keeps the bearings dry. Simply put you have the support bearings inside the hull, with a plain bearing, or nylon sleeve as the through hull.

I can't upload a sketch, so try to visualize.

You attach the framework to the hull with the shaft supported by ball bearings, then extending through thd hull using a bushing with rubber or plastic seals on the outer edge.

There will be some weepage, depending on depth and pressurization. If you're pressurizing the boat, then slight over pressure will bleed air out and prevent water from entering. Or you can use a box inside the thru-hull, and feed a small trickle of air so there's a positive outflow.

The basic design can be refined but the key is a between the bearing and a 2-3" sleeve as the through hull.

BTW the biggest challenge will be managing air. Whethet you opt to breath through a mask, try to recruit someone familiar with the physiology of underwater exercise, because it's different than on the surface.

I should have mentioned this is a "wet sub" aka the entire structure is flooded and they wear scuba gear when pedaling. I can buy multiple hubs (if that is the right term) and swap them out daily. Maybe wsterproof grease on the outside to prolong thr inevitable

Many bearings are commonly available in stainless (440C). I suspect that will be fine for the duration of training. Plan to replace them before the competition, and don’t worry about it. You could try to seal and pressurize them, but that’s just seal drag and probably not worth it for a one off.
Some of the plastic bushing companies used to sponsor those competitions. We never used them the the ASME bicycle competitions due to drag concerns, but they won’t corrode.
If you want to learn something interesting look up the designs behind the wet wooden bearings used in power plant turbines and at least one early nuclear submarine.

thx g or the reply. Its freshwater. I bought a stainless chain so will use that and may want to replace the steel cogs or maybe just paint them to help with corrosion. Good thought on the zinc. ​​​​​​​

Fresh water won't be too hard on the hub or chain. Note that rhe damage happens while things stay wet for hours after leaving the water.

So, marine grease, then use a heat gun or powerful hair dryer after each set of runs so the wet time is minimized.

You can also buy zinc powder, and blend it into the grease to add some extra time against corrosion.

FWIW, my road bike/touring bike has been submerged multiple times in floods and 1 lake. No damage or rust despite no special precautions or maintenance.
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Just out of curiosity ---- how long is the event?. I'm a diver and know what hard effort does to sir consumption.

Don't overthink this. Just grease your current bearings liberally with marine grease. A bit of water intrusion will not affect performance. If this is a multi day event, just plan on possibly having to tear down and regrease, but I really don't think this will be necessary because good marine grease should hold up.

Also, we want to see some pictures.

Good to hear it's freshwater. Money-wise, it's probably best to use marine grease in the bearings and after you remove the craft from the water, perhaps spray the chain, cogs and other unprotected surfaces with WD-40 or Boeshield T9 to displace the water and add a thin protective film.

At worst, you might get surface rust, but I highly doubt the corrosion will be severe in the time frame you describe.

Sacrificial anodes (zincs) work only when the system is submerged, and I'm guessing the total submersion time for the entire project is relatively short. So anodes are probably unnecessary.

just googled pics, wicked pissa! :thumb:

Anybody putting grease in a lake needs to be reported to EPA. IMO It will have ZERO benefit anyway. WTF are you thinking?? Another damn troll?

IMO - bearing grease is the least difficult design issue you'll have to address.

get in the caaah, go to a baaah and have a beaaah as my southie coast guard buddy henry would say

So every boat trailer, outboard, etc

This is a BICYCLE forum. NOT submarines, not hot-dog stands, not oddball scooters, not 100 yard dash nonsense.

So, if the OP had hidden his agenda by asking about lube or issues related to riding a bike in a flood, ie. the 4' depth I had to navigate, all would be OK?

Keep in mind, that it was only about the bicycle element ---- not the prop, air supply, floatation, etc. So not any different from a very legitimate inquiry.

Drill & tap the hubs for zerk fittings.
Pump with a grease gun until the water is forced out after each use or prior to storage as needed.

I commute in winter and often ride through slushy, sloppy, wet, salty brine, and for the last bunch of years using WD-40 to spray down my chain after a good rag wipe to get grit and as much water off after each ride, has been surprisingly successful in keeping the chain rust free.
Not the same total immersion thing, but its just an easy solution to keeping a protective film as noted on stuff, and of course doing the WD water displacement job. As noted above, never hurts to spray other stuff also post immersion after a wipe down.

the bottom bracket bearing is probably worth packing with grease as mentioned, but if it is not a ball bearing type bb, I guess just remove the cartridge bb and grease the heck out of the threads and everything--although as someone else noted, he'll probably be preoccupied with all of the actual designing, constructing and problem solving issues along the way, so if the mtb drivetrain is working, grease replacement and stuff will probably be pretty low down on the priority list.

I'm sure it will be a fun project to work on and try to minimize all the gearing friction points to get as much leg power to the prop

So you're volunteering to be a moderator?

I think the EPA has bigger things to worry about than a single underwater bicycle.
They have a whole satellite just to keep an eye on us

https://cimg4.ibsrv.net/gimg/bikefor...6d73f6dfe8.png

Hi, actual Subsea Vehicle Pilot/Tech here:


Unless this thing is staying underwater for weeks at a time, you don’t need to go to any extreme measures. Especially if it’s fresh water, galvanic corrosion happens way slower In fresh , and way slower than you all think it does, even in seawater.

Like it was mentioned above, it’ll be the most vulnerable to corrosion if it’s left wet after it comes out of the water. Rinse it when it comes out, and use compressed air (even a leaf blower) to get the water out of the nooks and crannies.
We also use a lot of wd40 on surfaces we don’t want water settling on (after we hit it with the air)

we use a lot of solid bronze bushings, with ceramic on the high-speed stuff like the thruster prop shafts. You’ll probably not need to withstand 200hp at 300 rpm, so the standard bearings in the hubs/cranks will be fine. I’d pack them full of blue “trailer” grease to keep the water out. We use that on a lot out here. Adding a zerk to keep them topped off is a good idea, just so you don’t have to tear them down every time you want to add grease.

If there’s a chain involved, we like White Lightning “Epic” chain lube (mfgr recommended) or in a pinch, the white lithium grease that comes in a spray can. It’s really more about getting lube between the side plates, than on the rollers.

Good luck with the project!

https://cimg1.ibsrv.net/gimg/bikefor...92c1696d3.jpeg

Is this for the International Submarine races at the David Taylor model basin in Carderock? I did that back in high school, we went with a bike drivetrain too. For the bearings, we just made sure to wash them off, sprayed them with WD-40 and put some fresh grease in before we left for the races. They lasted the whole weekend without any problems. I think the water they used in that basin was pretty fresh, so corrosion wasnt a big issue.
On a side note: we had problems with the chain skipping on the rear cassette of our bike drivetrain, so i reccomend increasing chain tension if you are using a derailleur, or better yet: go single speed and avoid the problem altogether.

to the Beezer mom or dad, it's nice to see the vast majority of friendly, helpful responses here.

re chain skipping--you would think this would happen due to an already "on the edge" worn chain and or cassette, quite possibly from a pretty worn out donor bike. We crank down pretty hard on drivetrains and don't have skipping unless there is a wear issue already. One would think that a derailleur tension underwater would be the same, and if it is securely set in the right position for a given cog, being immersed in water wouldnt be a factor (certainly dont have underwater drivetrain experience though)

may I suggest to make sure that the shifter/derailleur setup is very well adjusted on land, and try to eliminate a shifter than can "creep", I'm thinking of a really cheap thumbie shifter without enough tension.
Basically trying to eliminate any drivetrain issues before you deal with being underwater and dealing with all the other factors, buoyancy, maintaining a given upright position, and pedalling with enough prop rotation to have a given speed.

sounds like a real challenge, I'm sure it will be a fascinating experience for your son.